Laser Printer User Manual

1.2.3Howyour Iaserprinter communicates

YourcomputercommunicateswiththeStarLaserPrinter4 througheither

apardef cableoroneoftwokindsofserialcable.Theprinter’sinterjzce,

the link or boundaryit shares with your computer,defineswhetherthe

printerwillacceptcharactersandcommandsfromyourcomputeronebyte

or onebit at a time.

Abitisthesmallestunitof computerorprintermemory.Ithaseitheralow

orhighelectriccharge,whichwerepresentwiththedigitsOand 1.Usually

eight adjacentbits are groupedto form a byte. Since a byte normally

representsonecharacter,thisstringofbits- O1OOOOO1—mightrepresent

the letterA.

The serialinterfaceacceptsjust one bit at a timefromyour computer.A

parallelinterfacecanhandleawholebyteatonce,bymovingdatabitsside-

by-sidealongseparatewires.Youchoosewhichinterfacemethodyouwant

to useby selectingit onthe controlpanel,asexplainedin yourStarLuser-

Printer4 OperationsManual.

1.2.4 TheStar LaserPrinter4 is a computer

TheStarLaserPrinter4 firstmapsthecharactemto beprintedintoitsown

randomaccessmemory(RAM).Thatis, theprinterbuildsa “picture”inits

memorycorrespondingtothepageyouwanttoprint.Whenthat’sdonethe

printercanreproducethepageontopaperonitsown,lettingyourcomputer

geton withotherwork.

YourStarLaserPrinter4 comeswithonemegabyteofRAM—theequiva-

lentof aboutonemillioncharacters.A StarLaserPrinter4 optionlets you

addasecondmegabyteofRAMif,say,youneedtomapfull-pagegraphics

or stemmorefonts. AccompanyingallthatRAMis another512kilobytes

of readonlymemory(ROM),containingalibraryof internalfontsandthe

programsthatlet the StarLaserPrinter4 emulateotherprinters.

An Intel 80960KAcomputerchip controls both the memory and the

printingmechanisminthepnnter,calledtheprintengine.Theprinterstores

a whole page in RAM before printingit. (If a page is so dense that it

overflowsmemory-a mostunlikelyevent—theStarLaserPrinter4 prints

thepageon two sheets.)